1. Field of the Invention
The present invention relates generally to vascular grafts. More particularly, the present invention relates to woven or porous PET (polyethylene terephthalate) grafts having unique polyurethane coatings to improve resistance to permeability, useful in applications such as endolumenal repair of abdominal aortic aneurysm.
2. Description of Related Art
Abdominal aortic aneurysm (AAA) is a leading cause of death in the United States, causing an estimated 15,000 mortalities each year. An abdominal aortic aneurysm is a bulge in the wall of the artery, usually a sequela of arteriosclerosis or the buildup of plaque on the inside of the artery. If untreated, the aneurysm may rupture, causing death.
One approach for the treatment of AAA involves invasive abdominal surgery. The abdomen is opened and the aneurysm is identified. The aorta is opened and a surgical graft is inserted into the aorta and sewn in place. The aorta is then closed over the graft. More recently, stent grafts have been used in less-invasive procedures. Stent grafts include a graft layer inside or outside a stent structure. The stent graft provides a graft layer to reestablish a flow lumen through the aneurysm and a stent structure to support the graft and to resist occlusion or stenosis. Stent grafts may be inserted via incisions in the groin and deployed at the aneurysm site using a delivery catheter. Once in place, the stent graft expands within the aorta, providing a path for blood flow and reinforcing the weakened vessel. Examples of stent grafts are described in U.S. Pat. No. 6,015,431 to Thornton, et al. and published PCT International Application WO 98/27895.
A variety of materials have been used for vascular repair including PET (woven and knitted), Teflon®, bovine vessels, cryopreserved vessels of human or animal origin and others. Whether a traditional or stent graft, because of the size of the vessel being reinforced and the pressures within the vessel, AAA grafts must be made of strong and compliant textiles. Dacron®, or the more generic name, polyethylene terephthalate (PET), is an accepted and commonly used material for vascular repair, particularly for large diameter vascular grafts (>6 mm in diameter).
PET grafts are made in a similar fashion to most textiles. Fibers are woven or knitted into a specific geometry and structure. The result is a very strong “fabric” but one which is porous. Because integrity against leakage of the graft is important, such vascular grafts are often preclotted to prevent leaking. Alternately, graft pores have been sealed with collagen and other materials. However, although collagen and other coatings may provide sealing to prevent initial blood losses, known coatings have not proven adequate for more long term needs (>1-3 months) or cases where fluid (e.g., serum or water) permeability is important. The permeability of grafts is a particular problem in PET grafts for endolumenal AAA repair. Because of the porous nature and insufficiency of currently available coatings, over time seepage develops between the PET grafts and the aorta. In the case of AAA, permeability of the graft to any fluid can lead to worsening of the aneurysm.